System and method for television communication



Jan. 7, 1941. R 1 CAMPBELL 2,227,822

SYSTEM AND METHOD FOR TELEVISION COMMUNICATION Filed March 17, 1959 4 Sheets-Sheet l FIGJ FREQUENCY MULTIQLIER I I 264.60K1; |4 26,460

so PULSE N s ucnnoh RADIO GEN nA'romk I PHASE MIX N6 il-r GENERATOR uoouumon AMPLIFIER-QM w I2) 9 IG GENERATOR 5,230 I6 FIG 4 CAMERA I Q50 LmE RADIO AM ung AMPLIFIER TRANS I SYNCRO. l GENERATOR 4 l5 29 if ,gmcRoPHoNE AUDIO l3 FREQUENCY Mum PLIER PHASEMODULATOR AMPLIFIER 264-6 K.C- PHASE-MODULATED CARRIER LOCAL CARRIER INVENTOR L Jan. 7, 1941.

SYSTEM'AND METHOD FOR TELEVISION COMMUNICATION R. L. CAMPBELL 2,227,822

Filed March 17, 19159 4 Sheets-Sheet 2 FIG, 2

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AMPLIFIERS CDETEICTOR i -o l 8 I9 20 NVW g 0 VIDEO RECEIVER j I] A v FREQUENCY" 53:3. ZEJIRRIER 0 0 WE 6 (UNMODULATED) LZI DETECTOR IL 23 I31 HORIZONTAL T swEEP "1 AMPLIFIER o I VERTICAL G I oSWEEP I AMPL|F|ERo-" +250 INVENTOR RICHARD L CAMPB Jan. 7, 1941. R CAMPBELL 2,227,822

SYSTEM AND METHOD FOR TELEVISION COMMUNICATION Filed March 17, 1939 4 Sheets-Sheet 5 FREQUENCY PHASE I MUU'PUER 3 see 90 E- N mxms k-C. ll L33 36 LINE 1 AMPLIFIER --+--o b 9 "38 F M f-g- P. Wu. G 4

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SYSTEM AND METHGD FOR TELEVISION COMMUNICATION Filed March 17, 1939 4 Sheets-Sheet 4 RADiO Y RECEIVER FIG- 43 4 6 DETECTOR l s AUDIO 66.9K.C. c oerscmn sELEcm AMPLIFIER LOUD P K 42 45 5 EA ER v A ooeTEcTom. $25

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V A V 6 K-C I "s .|75 2K- 3,1o41 -c 3,966.9

INVENTOR Patented Jan. 7, 1941 SYSTEM AND METHOD Fon TELEVISION COMMUNICATION RichardL. Campbell, Ilasbrouck Heights, N. 1., assignor to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application March 1'1, 1939, Serial No. 262,327

18 Claims.

My invention relates to improvements in sys- Other objects and advantages will hereinafter appear.

In accordance with my invention, at the transmitter there is developed a carrier frequency and a line frequency, and these frequencies are harmonically related. There is also developed a field frequency. Saw-tooth waves, at the line and field frequencies, respectively, are obtained for 'the horizontal and vertical sweeps. phase-modulated with the vertical "sweep and mixed with the horizontal sweep at the line amplifier to the radio transmitter. At the receiver, a local carrier, which is not phase-modulated, is derived from the horizontal sweep signal, and is used for detection of the phase-modulated carrier.

Further, in accordance with my invention, at the transmitter a carrier of constant amplitude is phase-modulated only, with a signal such as the vertical sweep signal, or the horizontal sweep signal, or the sound signal. fixed harmonic irequency relation to the horizontal sweep signal. The phase-modulated carrier is mixed with one or more other signals at the line amplifier to the transmitter.

My invention resides in the improved system and method of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein Figure 1 is a simplified, block diagram or a television transmitter constructed and operating in accordance with my invention;

Figure 2 is a simplified, block diagram of a television receiver for the transmitter in Fig. 1;

Figure 3 is 'a simplified diagrammatic view showing a modification of the receiver in Fig. 2;

Figure 4 is a view similar to Fig. 1, showing a modification,

Figure 5 is a view similar to Fig. 1, showing a further modification; and

Figure'G is a. simplified, block diagram of a television receiver for the transmitter in Fig. 5.

With reference to Fig. l, a synchronizing generator l0 supplies a -cycle pulse for driving a The carrier is 1 'I'his carrier bears a (c1. lie-5.6)

saw-tooth wave generator I l for the vertical sweep at the field frequency. The generator llll also supplies a signal, at line frequency, for driving a saw-tooth wave generator II for the horizontal sweep. It will be understood that the two 5 saw-tooth waves are applied locally to deflect the cathode-ray of the transmitter tube 9, as represented. A signal at 26,460 cycles, is taken from the generator Ill and is multiplied e. whole number of times to 264.60 k. c. by a frequency mulm tlplier iii to obtain a sub-carrier wave in the output line M. The carrier frequency and the line frequency are harmonically related. The carrier signal in line H! is phase-modulated with the vertical sweep in a phase-modulator l5, and is mixed 5 with the horizontal sweep at the line amplifier It to the transmitter ll.

Since the 264.6 k. 0. carrier is of constant amplitude and is phase-modulated only, any cross-modulation effects will 'be materially less 30 than would be the case if amplitude modulation were used.

At the receiver, in 'Fig. 2, the 264.6 k. 0. carrier which is phase-modulated with the 60-cycle vertical sweep, is taken from the second detector 18 25 and applied to the grid 19 of a mixer tube 20. The horizontal sweep at the line frequency is obtained by using an elimination filter 2| to remove the 264.6 k. c. signal, and is amplified by an amplifier l 3 and applied to the horizontal defiect- 30 ing plates of the receiver tube 23.

A signal at line frequency is taken from the amplifier I3, and is multiplied to 264.6 k. c. to obtain an unmod'ulated local carrier which is applied to the mixer grid 24 of the tube 20. The 35 output from the mixer tube 20 is applied to the detector tube 25 from which the (SO-cycle sawtooth wave is obtained and after amplification applied to the vertical deflecting plates of the tube 23.

In the modification shown in Fig. 3, an amplifier tube 26 is used in place of the mixer tube 26. The 264.6 k. c. carrier which is phase-modulated with the (SO-cycle vertical sweep, is applied to the grid l9a which corresponds to the grid l9 in Fig. 2. 5 The unmodulated local carrier from the frequency multiplier is applied through a transformer 21 to the detector circuit shown, fronn'th-e output 28 of which is obtained the vertical sweep, or saw-tooth wave at the field frequency of 60 50 cycles.

In Fig. 4, the principle is the same as in Fig. 1, the difference residing in the fact that the subcarrier taken from the frequency multiplier I 3 is phase-modulated by the sound signals from the u audio amplifier 29, as represented, and in the line amplifier 13 is mixed with the video signals for transmission over the single R. F. channel.

In Figs. 5 and 6 the principle is also the same as before, the difference residing in the fact that all four signals, namely, the horizontal and vertical sweeps and-the video and sound signals, are transmitted on one and the same carrier. For this purpose, a master oscillator 30, which may becrystal-contr-olled, is used. From this oscillator, and by means of separate frequency multipliers 3|, 32 and 33, as many different sub-carriers are obtained, as indicated, each being harg,

monically related to the line frequency which is also obtained from the master oscillator 33 driving the synchronizing generator.

By means of a phase-modulator 34, the subcarrier from 3| is anodulated by the vertical sweep. By means of a phase-modulator 35, the sub-carrier from 32 is modulated by the horizontal sweep. By means of a phase-modulator 36, the sub-carrier from 33 is modulated by the audio signal.

The three phase-modulated sub-carriers and the video signals from amplifier 31 are mixed in the line amplifier 38 to the transmitter 39 and transmitted on a single carrier.

At the receiver, the phase-modulated sub-car riers are selected or separated out by the respective selectors 4!, 42 and 43, and the diflerent signals are detected by the detectors d4, 45 and 66, respectively.

A local carrier selector 41 supplies the respective local, unmodulated carriers, as represented, and which are applied to the corresponding detectors, as in Figs. 2 and 3. 1

The circuits or units l5, l6 and ii in Figs. 1 and 4, and 34, 35, 36, 38 and 39 in Fig. 5 are of any suitable, conventional construction. The generators ii and I2 in Fig. 1 and the corresponding generators in the other figures, may be generators of any suitable, conventional form to generate either a saw-tooth wave or a sine wave.

Since phase modulation is one form of frequency modulation, some of the claims herein use the broader term, and are not limited to a system wherein the operating action is specifically one of phase modulation.

It will be understood that various modifications, within the conception of those skilled in the art, are possible without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. In a television system, a generator of synchronizing signals at a given field frequency and at a given line frequency respectively, means for multiplying the line frequency a whole number of times to obtain a carrier frequency, a generator of an electrical sweep wave driven by the sign'ais I k the field frequency and driven by the signals at the field frequency, and a phase-modulator for modulating the carrier frequency bysaid electrical wave.

3. In a television system, means for obtaining a line frequency, means-for multiplying the line frequency, .means later for modulating the carrier frequency by the sound signals. k v

4. In picture-reproducing apparatus means for intercepting a frequency-modulated sub-carrier and a carrier modulated by a line frequency, 5 means for detecting the line frequency, means for multiplying the detected line frequency to obtain a local carrier, and means utilizing said local carrier for detecting the frequency-modulated cartier.

5. In a television system, a generator of synchronizing signalsat a. given field frequency and at a given line frequency respectively, means for multiplying the signals at the line frequency to obtain a carrier frequency, a generator of an electrical wave driven by the signals at the field frequency, and a phase-modulator for modulating the carrier frequency by said electrical wave.

6. In a television system, means for obtaining a field frequency and a line frequency, means for multiplying the signals at the line frequency to obtain a carrier frequency, a generator of an electrical wave at the field frequency and driven by the signals at the field frequency, and a phasemodulator for modulating the carrier frequency 25 by said electrical wave.

7. In a, television system, means for obtaining a line frequency, means for multiplying the line frequency to obtain a carrier frequency, means for obtaining video signal means for generating 30 sound signals, a phase-modulator for modulating the carrier frequency by the sound signals, and means for mixing the modulated carrier frequency and the video signals to obtain a composite signal.

8. In a television system, a generator of synchronizin'g signals, means for multiplying said synchronizing signals to obtain a carrier frequency, a generator of a sweep wave driven by said signals, and a phase-modulator for modulating the carrier frequency by said sweep wave.

9. In a television system, means for generating signals harmonically-nelated to a given line fresignals harmonically-related to a given line frequency, means for multiplying said signals to obtain a carrier frequency, means for obtaining an electrical eife'ct for synchronizing purpose, and frequency-modulating means for causing the carrier to be frequency-modulalted 'by said electrical efiect.

12, In a television system, means for generating signals harmonically-related to a given line frequency, means for multiplying said signals to obtain a carrier frequency, means for generating video signals, means for generating sound signals, frequency-modulating means for causing the carrier to. be frequency-modulated :by said sound signals, and means for mixing the modulated carrier frequency and the video signals to obtain a. composite signal.

13. In a television system, means for generating signalsharmonically-related to a given line fre- 76 quency, means for multiplying said signals to obtain a carrier frequency, means for generating video signals, means for obtaining an electrical efi'ect for synchronizingpurpose, frequency-mod ulating means for causing the carrier to be frequency-modulated by said electricaleffec't, and means for mixing the modulated carrier f requenoy and the video signals to obtain a composite signal.

14. In a television receiver, means for intercepting a sub-carrier frequency-modulated by a sweep wave and for intercepting a carrier modulated by a line frequency, means for detecting the line frequency, means for multiplying the detected line frequency to obtain a local carrier, and means utilizing said local carrier for detecting the frequency-modulated carrier whereby the and means utilizing said local carrier for detecting the frequency-modulated carrier whereby the sound signals are obtained.

16. In a. television receiver, means for intercepting a sub-carrier frequency-modulated by an electrical synchronizing effect and for intercepting a carrier modulated by a line frequency, means for detecting the line frequency, means for multiplying the detected line frequency to obtain a. local carrier, and means utilizing said local carrier for detecting the frequency-modulated carrier whereby the electrical synchronizing effect is obtained.

17. In the art of picture-transmission wherein a given electrical eflect is utilized for reproduction of the transmitted view, the steps in the method of operation which consist in generating a signal the frequency of which is harmonlca'lly-related to a given line frequency, multiplying said signal to obtain a carrier, and transmitting said electrical efiect on said carrier 'by frequency-modulation.

18. In the art of picture-transmisslon'wherein there is transmitted to the receiver a carrier Ire quency-modul-ated by an electrical efiect, the steps in the method of operation which consist in obtaining at the receiver a. signal the frequency of which is harmonlcally-related to a given line frequency, multiplying said signal to obtain acarrier local to said receiver, and utilizing said local carrier to detect the frequencymodulaited carrier whereby said electrical efiect is obtained at the receiver.

RICHARD L. CAMPBELL. 

